1. Field of the Invention
This invention relates to suspension systems for automobiles as well as machines which receive mechanical shock, and more particularly to a base valve for a shock absorber.
2. Description of Related Art
Shock absorbers are used in connection with automotive suspension systems to absorb unwanted vibrations which occur during driving. To dampen unwanted vibrations, shock absorbers are generally connected between the body and the suspension of the automobile. A piston assembly is located within the shock absorber and is connected to the body of the automobile through a piston rod. Because the piston assembly is able to limit the flow of damping fluid within the working chamber of the shock absorber when the shock absorber is compressed or extended, the shock absorber is able to provide a damping force which "smooths" or "dampens" vibrations transmitted from the suspension to the body. The greater the degree to which the flow of damping fluid within the working chamber is restricted by the piston assembly, the greater the damping forces which are generated by the shock absorber.
Because the amount of damping forces the shock absorber generates causes variation in driving characteristics, it is often desirable to have a shock absorber in which the amount of damping forces generated by the shock absorber is adjustable. One method for selectively changing the damping characteristics of a shock absorber is disclosed in PCT International Publication No. WO 88/06983. This reference discloses a shock absorber which has a solenoid for controlling the flow of damping fluid into pressure chambers which are located adjacent to valve disks which control the damping characteristics of the shock absorber. Upon movement of the plunger of the solenoid, the pressure in these pressure chambers changes so that the damping characteristics of the shock absorber may be varied.
Another method for selectively changing the damping characteristics of the shock absorber is disclosed in U.S. Pat. No. 5,016,908 reference, the plunger of a solenoid extends into the body of the piston and is used to control the flow of damping fluid through flow paths which lead to two unloaders which are able to bias upper and lower spring disks. By controlling the flow of damping fluid through these flow paths, it is possible to vary the damping forces generated by the shock absorber.
Shock absorbers which are used to provide variable damping often have a base valve which controls the flow of damping fluid between the lower portion of the working chamber and the reserve chamber which surrounds the pressure cylinder in which the piston is located. While such base valves generally serve their intended purpose of controlling the flow of damping fluid between the reserved chamber and the working chamber, they often do not adjust the flow of damping fluid in response to the desired damping characteristics which the shock absorber is to provide. In other words, these base valves would typically allow approximately the same amount of damping fluid to flow between the lower portion of the working chamber and the reserved chamber regardless of whether the shock absorber was to provide firm damping or soft damping.